The Window / Level tool allows modifying the Window Width and Window Level values for the gray levels (or colors) of the current image. The Window,Level values are given in Hounsfield Units if the selected image panel contains a CT image. You may change the Window,Level values by dragging with the associated mouse button over the image.
The Tool Options panel associated with this tool is shown in the picture below:
If the Apply to series toggle button is pressed (i.e., selected) then the Window / Level changes will be applied to the entire series.
It is also possible to change the sensitivity of mouse dragging movements for contrast changes, by dragging the Sensitity slider in this panel.
Window Width and Window Level values can also be changed by dragging the mouse pointer on the Window / Level widget (the square with a black background). Right-clicking on the Window / Level widget causes restoring the Window,Level values contained in the DICOM file (if they are present). You may also change the Window,Level values by selecting one of the available contrast Presets (from the Presets drop-down list). Finally, you can manually enter Window,Level values in the W / W and W / L text fields, and press ENTER on your keyboard to confirm and apply them.
Press the Auto button in order to apply an automatic “optimal” windowing for the currently selected image. The Reset button may be used to restore the original Window,Level setting suggested in the DICOM data set (if present).